Vintage Modem Connection Problems

[Electricdreams]

Since finding a BBS number, I dug out my Pace Nightingale Modem connected to a BBC master 128 and dialled up to a BBS server.

It does receive data, all clear no jumbles, but it would stop unexpectedly while receiving. So sometimes I would get a bit of the menu but not all.

At first I thought it might be my ADSL router, so I unplugged that and tried again, the issue is still there. I even tried experimenting different baud rates, parity, handshake and all sort of configurations but it did not make it any better.

So I decided to check this on a Powerbook 1400c laptop with a PCMCIA Modem and apparently haven't experienced any problems with the right baud, data & parity as the BBC.

So I decided to dig out my Epson CX-21 modem and connected that to my 286 laptop and used windows 3.1 terminal, unfortunately I received the same problem on that as well.

Has anyone experience any problems connecting to a BBS server? Does anyone have a list of troubleshooting for a beginner with a modem?

[AndiiT]

Hi,
Just a thought, but do you have the "call waiting" facility on your phone line? If so it may be that the call waiting tone is causing the modem to drop out when someone attempts to ring you.

Other causes could be that the modem is polarity sensitive (although it shouldn't be) this can be easily checked by transposing the A and B legs at the phone socket which the modem is connected to.

Many years ago cable companies experienced all sorts of odd problems with dial up modems and one of the "fixes" was to insert a couple of 300 ohm resistors in series with the A and B legs of the incoming exchange line - if you are some distance from the exchange this may make things worse though as most cable companies had relatively short lines from the multiplexer equipment to the subscriber, unlike BT/the GPO whose lines were often a few miles long and were correctly compensated for during installation.

Regards

Andrew

[Electricdreams]

Hi Andrew,

I don't have call waiting facility,

The Epson CX-21 is acoustic coupler modem so would that rule out the sensitivity?

Would I need to contact BT and ask them to service my line?

Perhaps my modems are too sensitive?
I wonder because they are old they need servicing?

[G6Tanuki]

Dial-up modems do sometimes have 'issues' with 21st century phone infrastructure.

Thing is, for the last few years the analog voice phone system has worked on the principle of "digitize the signal as soon as possible then send it over an IP network until the nearest point to the recipient before converting it back to analog".

Which works fine for speech but has problems with 'audio' from modems etc.

This was even an issue in the late-1990s; a lot of ISPs installed what were colloquially known as "not-modems" in exchanges to split off the traffic to their ISP dialup-numbers and trunk it back to their infrastructure digitally without it being subject to the whims of the telco's multiple encoding/decoding. This was the only way to offer 56Kbit/sec dialup on old style analog lines

There was also an issue associated with BT's way to provide extra phone-lines in areas where the cabling was already at full capacity: they used a thing called a "DACS" to run two customer-facing phone outlets over a single wire: essentially this was a kind of multiplexer/compresser - see http://en.wikipedia.org/wiki/Digital...Carrier_System

These caused all sorts of horrors and did not play well with either dialup-modems or fax-machines.

[Electricdreams]

Thanks, thats very useful, I will have a look to see if I have one.
Will Mobile phones have the same effect?

I am deaf, so I am forced to communicate over the telephone via typetalk, now called Text-relay (18001) they use a similar system as modem and CCITT. I never had any problems with my text-telephone.

So I will experiment with the modem to see if there is a fault on typetalk and will report on here.

[Electricdreams]

I've just tested with the speaking clock and it works fine, there isn't a problem with the buffer. So perhaps it was just a data overload on the modem? Is there such a thing?

[mike_newcomb]

Hi Idler, there is such a thing as data overload and it is managed by 'flow control'.
If not managed you lose data, which looks to be your problem.

I find your original post a little unclear, as it seems to suggest everything works ok, when using the Powerbook 1400.

Personally I do not have experience of the PACE and BBC, and therefore would use the 286 for testing. If possible with dos as the os. From Googling, the PACE appears to be a 300 baud asynchronous modem, alternatively 1200/75 Viewdata Modem.

Without going back into my archives, I cannot be precise the details below are 100% correct.

The MODE command is important. See:-
http://www.csulb.edu/~murdock/mode.html
Think retry has to be set to ,P

If the modem is external and connected to a serial port, cable connections are involved for RTS/CTS etc. Think around 6 connections minimum are required.

There may be more than one handshaking method provided between modem and pc.
So if these are provided as options, both ends must be selected to use the same method.
e.g. I used RTS/CTS (never XON/XOFF)

Some modems can be controlled 'inflight' using AT commands. Thus is you have a 'dumb terminal emulator in the pc, you can control the modem at the same time as sending and receiving data.

Can you provide more details for the BBS itself.
Am interested in its connection method(s).

Good Luck - Mike